The present invention relates to a hydropneumatic and, in particular, an oleopneumatic vehicle suspension element for heavy vehicles such as armoured vehicles.
It is known that an oleopneumatic suspension element comprises a piston movable in a cylinder, a gas accumulator connected to the cylinder and containing gas and a liquid separated from the gas by a flexible diaphragm, and a damping cartridge placed in the liquid between the piston and the diaphragm.
The shock absorption is achieved in an elegant and convenient manner by constraining the oil to pass through diffusers of the cartridge thereby creating, upon displacements of the piston in one direction or the other, a pressure drop which increases with increase in speed.
This dissipation has two consequences:
(a) It heats the oil, and thus limits the utilization of the suspension element to a maximum temperature imposed by the mechanical parts (joints, diaphragms) which are sensitive to these temperatures. In practice, this limit temperature of the oil is about 140.degree. C.
(b) It heats the gases of the accumulator (nitrogen), and thus increases the mean pressure of operation of the element. Consequently, by reaction, there is a variation (increase) in the height of the chassis of the vehicle above the ground, i.e. its ground clearance. Such a variation in the ground clearance may also be produced, although on a smaller scale, by large variations in the atmospheric temperature.
Consequently, the temperature of the oil must be limited so that it is correspondingly possible to maintain the height of the chassis of the vehicle above the ground substantially constant. For this purpose, there has been proposed a device for cooling the whole of the suspension formed by a series of these elements, by cooling the oil of the latter. Moreover, it is attempted usually to cool simultaneously the oil of all the elements constituting the suspension. But such a device requires a specific cooling installation comprising a pump and a radiator which is expensive and unreliable. Oil injecting systems have also been employed which use a central hydraulic unit. This central unit is expensive and unreliable. Indeed, in the event of leackages or breakage of the oil injecting piping, the suspension is put out of use. Further, it is in practice relatively difficult to inject oil in an oleopneumatic suspension element during the operation of the latter.